1. Field of the Invention
This invention relates to yarn texturing machines, and in particular to textile machines for the texturing of yarns by means of fluid jets.
2. Discussion of the Background
Textile machines are known in which one or more yarns are fed in single, parallel or core/effect form to a fluid jet in which the turbulent fluid serves to cause the filaments of the yarns to form loops, thereby producing a bulky single or composite yarn suitable for various textile applications. To facilitate this process a yarn wetting device may be located immediately upstream of the fluid jet, acting on some or all of the yarns, and in such cases the yarn wetting device and the fluid jet are customarily housed in a common housing or "jet-box". With parallel and, more especially, core/effect arrangements, in order to ensure acceptable texturing of the yarn, it is necessary that any yarn which runs through the wetting device is kept apart from the other yarn or yarns until they come together in the fluid jet itself. If this is not done, entanglement of the filaments of the yarns can take place upstream of the fluid jet, and this prevents or inhibits the texturing of the yarn. To prevent such prior entanglement it is usual to have guides for the two yarns at the entry of the jet-box and also on the body of the jet itself. These guides, whilst keeping the paths of the yarns separate, also provide changes in direction of travel of the yarns, with consequential increases in yarn tension as a yarn travels around a guide. Hence the yarn tensions prior to entry to the jet box may be considerably less than those at entry to the jet itself. Since the tensioning effect of the fluid jet is reduced as the yarn throughput speed increases an upper limit of yarn throughput speed occurs when the yarn tensions upstream of the jet box input guides fall to a level at which threadline instability occurs. To avoid such a problem it is known to feed the two yarns in spaced but converging straight yarn paths from the feed means to the air jet, for example in U.S. Pat. No. 4608814. Such an arrangement eliminates the change in yarn tension along the yarn path. In this prior patent the angular separation of the yarns is specified as being preferably in the range of 8.degree. to 25.degree.. However, at current high processing speeds the yarn tensions upstream of the air jet are low and it has been found that the abovementioned entanglement of the yarns can occur with such an arrangement. It has also been found that too large an angular separation of the converging yarns leads to deterioration in the quality of the resulting textured yarn.